There are two kinds of standpoints on the mechanism of hydraulic fracturing of soils

that are tensile failure and shear failure. Vast studies on the fracture mechanism as well as the corresponding theoretical formula of the fracture pressure appeared in literatures

however

their explicabilities were still not yet fully discussed. The computing methods of the fracture pressures for tensile failure and shear failure in three dimensional stress states are put forward in this paper. Base on Mohr-Coulomb failure criterion

the applicability of the proposed fracturing pressure calculating method is discussed. The results indicate that the hydraulic fracture criterion is related to the minor principal stress and undrained shear strength of soil; and the possibility of shear failure increases with the minor principal stress σ3 increasing. The hydraulic fracture test results in literatures verify the applicability of the proposed method.